1. Field of the Invention PA1 2. Description of the Related Art PA1 1. In use, a plurality of pressure gauges are needed for attachment to the pneumatic tires of a vehicle, respectively. Since each of the pressure gauges incorporates a signal transmitting unit and a power source, the tire pressure indicator is relatively expensive to implement. PA1 2. The pressure gauges are relatively complex in construction and are bulky. PA1 3. The receiver device receives the first and second codes wirelessly from the different pressure gauges. Such wireless transmission is susceptible to signal interference that can lead to improper operation of the tire pressure indicator. PA1 4. Since the pressure gauges are attached to the inflating valves of the pneumatic tires, they are exposed when in use and are easily subject to damage or theft. PA1 a pressure-responsive resonant switching device adapted to be mounted on the pneumatic tire and switchable among a first impedance state, where the pneumatic tire is under-inflated, a second impedance state, where the pressure in the pneumatic tire is within a predetermined normal operating pressure range, and a third impedance state, where the pneumatic tire is over-inflated; PA1 an excitation unit adapted to be mounted on the vehicle body adjacent to the pneumatic tire; and PA1 a controller connected to the excitation unit and operable so as to supply an excitation signal to the excitation unit in order to enable the excitation unit to co-act with the resonant switching device by virtue of mutual induction according to the impedance state of the resonant switching device for inducing current in the resonant switching device as the resonant switching device is moved so as to be proximate with the excitation unit due to rotation of the pneumatic tire relative to the vehicle body, the controller monitoring an output signal from the excitation unit and detecting presence of a change in the output signal of the excitation unit due to inducing of the current in the resonant switching device during a complete cycle of rotation of the pneumatic tire to enable the controller to determine the pressure condition in the pneumatic tire. PA1 a set of pressure-responsive resonant switching devices adapted to be mounted respectively on the pneumatic tires, each of which is switchable among a first impedance state, where the respective one of the pneumatic tires is under-inflated, a second impedance state, where the pressure in the respective one of the pneumatic tires is within a predetermined normal operating pressure range, and a third impedance state, where the respective one of the pneumatic tires is over-inflated; PA1 a set of excitation units adapted to be mounted on the vehicle body adjacent to the pneumatic tires, respectively; and PA1 a controller connected to the excitation units and operable so as to supply an excitation signal to each of the excitation units in order to enable each of the excitation units to co-act with a respective one of the resonant switching devices by virtue of mutual induction according to the impedance state of the respective one of the resonant switching devices for inducing current in the respective one of the resonant switching devices as the respective one of the resonant switching devices is moved so as to be proximate with the respective one of the excitation units due to rotation of the pneumatic tires relative to the vehicle body, the controller monitoring an output signal from each of the excitation units and detecting presence of a change in the output signals of the excitation units due to inducing of the current in the respective one of the resonant switching devices during a complete cycle of rotation of the pneumatic tires to enable the controller to determine the pressure condition in each of the pneumatic tires. PA1 a pressure-responsive resonant switching device adapted to be mounted on the pneumatic tire and switchable between a first impedance state, where pressure in the pneumatic tire is within a predetermined normal operating pressure range, and a second impedance state, where the pressure in the pneumatic tire is not within the predetermined normal operating pressure range; PA1 an excitation unit adapted to be mounted on the vehicle body adjacent to the pneumatic tire; and PA1 a controller connected to the excitation unit and operable so as to supply an excitation signal to the excitation unit in order to enable the excitation unit to co-act with the resonant switching device by virtue of mutual induction according to the impedance state of the resonant switching device for inducing current in the resonant switching device as the resonant switching device is moved so as to be proximate with the excitation unit due to rotation of the pneumatic tire relative to the vehicle body, the controller monitoring an output signal from the excitation unit and detecting presence of a change in the output signal of the excitation unit due to inducing of the current in the resonant switching device during a complete cycle of rotation of the pneumatic tire to enable the controller to determine the pressure condition in the pneumatic tire.
The invention relates to the detection of pressure condition in a pneumatic tire, more particularly to an apparatus that employs a pressure-responsive resonant switching device in a pneumatic tire to co-act with an excitation unit on a vehicle body by virtue of mutual inductance in order to permit detection of the pressure condition in the pneumatic tire.
Periodic monitoring of the pressure condition in a pneumatic tire is an important task for every car driver to ensure the safety of the vehicle. If an under-inflated tire condition exists, undue wearing of the pneumatic tire can easily occur and can lead to instability of the vehicle. In the event of an over-inflated tire condition, the pneumatic tire might explode while the vehicle is in motion.
U.S. Pat. No. 5,289,161 discloses a tire pressure indicator capable of generating an alarm signal whenever a pneumatic tire is under- or over-inflated. The tire pressure indicator includes a pressure gauge that has a casing attached to the pneumatic tire. A spring-loaded push rod in the casing of the pressure gauge moves, in response to the pressure of air that enters into the casing, between a first position in which the air pressure is below a predetermined low pressure limit, and a second position in which the air pressure is above a predetermined high pressure limit. A signal transmitting unit is provided in the casing of the pressure gauge, and has first and second switching devices which are controlled by the movement of the push rod. The first switching device activates the signal transmitting unit to transmit a first code when the push rod is in the first position, whereas the second switching device activates the signal transmitting unit to transmit a second code when the push rod is in the second position. A receiver device activates a first light emitting unit upon reception of the first code, and a second light emitting unit upon reception of the second code.
The aforementioned tire pressure indicator has the following drawbacks: